During the Global Tropospheric Experiment (GET)--Amazon Boundary Layer Experiment (ABLE) 2B campaign in the Amazon basin, samples of rainwater and throughfall were obtained in a ''terra firma'' (nonflooded forest) rain forest at the Ducke Reserve (2¿57'S, 59¿58'W). The samples were collected during one wet period (April 1 to May 13, 1987) and one dry period (August 1 to October 1, 1987). All samples were analyzed for Na+, K+, Mg2+, Ca2+, NH+4, Cl- and SO2-4, and pH. The rainwater was acidic, with a volume-weighted mean pH of 4.6 for the two periods. Rainwater input from the dry period was 2 times greater for Na+, Mg2+, NH+4 and SO2-4 and about 4 times greater for K+ than from the wet period. The ionic concentrations in throughfall were higher than those in rainwater, except for NH4+ during the dry period. This enrichment of throughfall is attributed to the interaction of precipitation with the forest canopy.